Can I change my instalment plan anytime?

For the most part, yes.

However, we have a billing cycle at the start of every month where the option will become unavailable.

For example, direct debit customers can replan any transaction up until the 3rd, where as customer's without a Direct Debit have until the 5th of the month. Bear in mind that these dates fluctuate due to weekends and bank holidays, so always check your main page of the app for your payment due date.

For more information about Direct Debit, instalments and payment dates, see this article.